College professor Francine Busby, a Democrat who took 36 percent of the vote in 2004 against Cunningham, has a large lead over the crowded field of Republicans running in what should be a comfortably Republican district. President George W. Bush won here in 2004 with 55 percent of the vote, eleven percent better than he did statewide, and as of January 2006 44 percent of the district's registered voters were Republicans compared to just 30 percent Democrats.

Polling has shown Busby between 40 and 45 percent of the vote -- within sight of capturing the 50 percent she would need in the open primary to avoid a June 6 runoff with the top Republican vote getter.

As the top-tier Republican candidates continue to spend their time and money attacking each other in hopes of advancing to a runoff against Busby, the National Republican Congressional Committee stepped into the void last week with an ad designed to soften up the Democrat. "She's been able to build momentum," acknowledged NRCC Chairman Tom Reynolds (N.Y.) in a briefing for reporters Friday. "At the end of the day we wanted to level the playing field in the general election."

The NRCC commercial, which is running in the San Diego media market, casts doubts on Busby's reformer credentials, stating that she has taken campaign contributions from a variety of lobbyists, including former Arizona Sen. Dennis DeConcini (D) who donated $500 to Busby. DeConcini retired from the Senate after three terms in 1994 and was caught up in the "Keating Five" scandal (along with fellow Arizonan John McCain). DeConcini was never formally charged for his role but was scolded by the Senate Ethics Committee.

The NRCC is spending $450,000 on the ad buy, and an additional $20,000 on direct mail and phone banks designed to ding Busby's image. Although Reynolds insists the ads are aimed at the general election, they could also have the effect of peeling away some of Busby's support in today's primary -- keeping her under that crucial 50 percent mark.

Thanks to a wrinkle in the Bipartisan Campaign Reform Act, the Democratic Congressional Campaign Committee is offering a helping financial hand to Busby as she seeks to fend off the impact of the NRCC ads. Businessman Eric Roach (R) has donated $2 million of his own money to his campaign, triggering the "millionaire's amendment" -- allowing Roach's rivals to raise money at increased limits and the DCCC to provide more coordinated funds directly to Busby's campaign. (Roach and former Rep. Brian Bilbray are considered the favorites to capture the most votes among the crowded Republican field today.)

The NRCC's anti-Busby ads are running at 1,400 gross ratings points in the San Diego market -- meaning that the average viewer will see the ads 14 times in a week. Busby's ads coupled with the DCCC supplemental spending brings her total spending on television to 1,361 gross rating points.

As of mid-day Friday, approximately 50,600 ballots has been cast -- with Republican ballots (23,637) outdistancing Democratic ballots (18,371) by roughly 5,000. Remember, however, that because of California's open primary, a Republican could vote for Busby and a Democrat could support one of the 14 Republican seeking the nomination.

While Democratic strategists insist publicly that Busby could well win a June 6 runoff against a single Republican, privately they acknowledge that today represents their best chance of winning the seat. An outright win -- or a showing in the high 40s -- by Busby would fuel the idea that 2006 will be a very good electoral year for Democrats. Anything less will give Republicans a talking point to deflate the Democrats' "culture of corruption" pitch to voters.

Polls in California don't close until 11 p.m. eastern time. Check The Fix tonight or tomorrow morning for results.